*Purpose: Describe correlations between pre-transplant (PreTXP) presence of anti-angiotensin II receptor type 1 antibodies (AT1R Ab) and post-transplant (PostTXP) outcomes in a pediatric kidney transplant (PKT) cohort.

*Methods: PKT patients (&lt 18 years of age) transplanted consecutively by University Hospital between 2013 and 2019 received retrospective AT1R Ab screening in immediate pre-transplant serum samples by commercial ELISA. Statistical associations between PreTXP AT1R Ab detection levels, rejection (one year and lifetime), induction type, donor type (deceased or living), pre-formed anti-HLA donor-specific antibodies (HLA-DSA) and development of de novo HLA DSA PostTXP were observed. HLA-DSA determinations relied upon luminex single antigen bead identification assay and were positive at &gt 1000 mean fluorescence intensity (MFI). Patients were excluded if PreTXP samples were unavailable or if PostTXP data points were unavailable. Univariate and multivariate statistical analysis were performed using JMP and GraphPad software.

*Results: 107/114 PKT patients met inclusion criteria for AT1R Ab testing and statistical evaluation. The PKT population was majority Hispanic (60%). PreTXP AT1R Ab detection revealed 75% of PKT had borderline and positive levels of Ab (27 negative &lt 10 U/ml, 31 borderline positive 10-17 U/ml, 49 positive &gt 17 U/ml). The majority of PKT involved first-time recipients 97%(104), Basiliximab induction 74%(79), deceased donation 91%(97) and absence of pre-formed HLA-DSA 86%(92). Antibody-mediated rejection (AMR) within the first-year PostTXP occurred in 3%(3) of the cohort; while AMR at any postTXP time occurred in 59%(63) of PKT. PostTXP de novo HLA-DSA were detected in 46%(49) of PKT. Only presence of HLA-DSA correlated with rejection endpoints. No significant association between AT1R Ab detection and PKT rejection was observed. Similarly, there was no correlation between AT1R Ab PreTXP detection and creatinine levels, creatinine clearance or changes in creatinine levels over time. There was a trend of correlation between presence of AT1R Ab &gt 10 U/ml PreTXP and patients that developed de novo DSA. Rejection and de novo DSA formation were not statistically influenced by race, induction, donor type or presence of pre-formed HLA-DSA.

*Conclusions: Contrary to other studies of AT1R Ab detection in PKT, detection of PreTXP AT1R Ab did not correlate with rejection in our cohort. There is evidence that PreTXP screening for AT1R Ab could correlate with increased likelihood of de novo HLA DSA development PostTXP in PKT. This study supports screening of AT1R Ab PreTXP in PKT candidates.

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